91av

IN AN animal hospital 50 kilometres west of Berlin, a thoroughbred mare is in torment. She staggers around in circles. She presses her head mournfully against the stable wall. When a vet places one of her limbs across the other, she doesn’t correct her gait as any healthy horse would, but remains cross-legged, head hung low. There is no hope for this horse, and only one kindly course of action. A quick injection. She sinks into the straw, and dies.

One more horse succumbs to Borna disease: a fairly unremarkable event in this part of Germany. The sickness was named a century ago, when 2000 cavalry horses died similar, miserable deaths in the town of Borna. And it’s been known since the 1920s that the horse killer is a virus. But now, in the 1990s, a much weirder tale is emerging.

Borna disease virus, it turns out, may infect not only horses, but people too. And two virologists, Hanns Ludwig at the Free University of Berlin and Liv Bode at Berlin’s Robert Koch Institute, are making the controversial claim that Borna virus may cause more than half the cases of clinical depression in humans. They also claim to have the drug that will wipe out the infection. “There is no doubt now that the virus can get into humans and cause psychiatric disease,” says Ludwig. “And we are on the way to a cure.”

Human strain

Human psychiatric disorders caused by a horse virus? Mental illness cured by killing that virus? In the last few years, Bode and Ludwig’s published reports have come fast and furious. In 1994, they found Borna virus protein in the blood of people with clinical depression. In 1995, they found traces of Borna virus RNA as well. Then, in 1996, they finally managed to extract Borna virus from the blood of three mentally ill patients- two with acute depression and a third with obsessive-compulsive disorder. When they infected rabbits with that virus, the animals promptly became sluggish and withdrawn. Bode and Ludwig also sequenced the virus’s genome, and concluded that it was a bona fide human strain of Borna albeit very similar to the strains that usually infect other creatures.

Last January, though, came the big splash. Bode, Ludwig and their team reported in The Lancet that the drug amantadine, which is used to treat people with Parkinson’s, stops Borna virus from multiplying in human brain cells in a dish. When they gave the drug to a woman with bipolar disorder who was in the acute, depressed phase of her illness, it both swept away her symptoms and all traces of the virus in her blood. “It was very exciting to see these two things happen together,” says Bode. “And we now have other cases just like the one we published.”

No wonder telephones have been ringing off the hook in Borna labs all around the world, with urgent pleas for help. Bode and Ludwig say they warn such callers that Borna virus is unlikely to be the sole culprit in clinical depression, bipolar or otherwise. Other factors, such as genetic predisposition and the travails of life, will weigh in as well. Still, they’re convinced enough by their findings to have joined forces with psychiatrists in Hanover to set up a clinical trial comparing amantadine with a placebo in 40 clinically depressed patients. “I’m very enthusiastic about this,” says Bode.

“Enthusiastic” is not the word for the reaction of other Borna virus scientists. “Irked” would be more accurate. At least four other research groups have now tried using amantadine to prevent Borna virus replicating in tissue culture. And two have tried the same trick in rats and mice infected with the virus. All report failure. What’s more, they say, if amantadine does cure certain cases of depression, it may not do so by knocking out Borna. One group of psychiatrists and researchers, led by Klaus Lieb at the University of Freiburg, went as far as to fire off a letter to The Lancet that appeared this March. They wrote that amantadine’s antidepressant effect is well known, but most of the evidence suggests that the drug works by binding to an important receptor in the brain, the NMDA receptor, and not by destroying virus.

Drug dealings

“If the woman felt better, it doesn’t say anything,” says Lothar Stitz, a Borna researcher at the Federal Research Centre for Virus Diseases of Animals in Tübingen. “I have problems with The Lancet accepting a paper like that. I’ve had many phone calls, from doctors, from patients with depression, saying `How can I get the drug, where can I buy it? I need it for my mother, my son, for my whatever.’ There are so many hopes evoked that may never be met.”

Other Borna researchers complain that it’s premature to be considering drug therapy, because there is still no sign of any agreement on whether or not the virus really does infect humans or cause mental disorders. “It’s extremely controversial, the whole thing-it gets some people very agitated indeed,” says Juan de la Torre, a virologist at the Scripps Research Institute in La Jolla, California. “You have serious investigators who think the whole thing is bogus; there are others who think that the virus does cause neuropsychiatric disorders. Then there are people like me, and quite a few others, who say well, it’s really too early to say anything.”

Up until the 1980s, the science of Borna virus was a strictly nonhuman affair. First found in horses, it was later shown to naturally infect sheep, cattle, cats and ostriches. In the lab, scientists extended the range to rats, mice, chickens and rabbits, as well as tree shrews, which are primitive primates, and rhesus macaques. Sometimes animals would die from severe brain damage, and sometimes they wouldn’t, depending on how and when they were infected. But in all cases, the virus settled in the parts of the brain that modulate basic emotions (the hippocampus and hypothalamus, for example), and caused strange behaviour, including aggression, apathy, altered sexual habits, and changes in social pecking orders.

If the virus infects such a wide range of animals, including primates, then it’s not a big leap to propose it might also infect people. And if it does, what’s to stop it messing with our minds just like it does with animals, causing schizophrenia, perhaps, or depression? So ran the perfectly logical reasoning, and in 1985, the notion got its first, tantalising glimmer of support. That year, a US-German research team led by Rudolf Rott of the University of Giessen drew blood from 979 assorted psychiatric patients, and 200 “normal” controls. Then they tested the samples for antibodies to Borna virus-in other words, for signs that the virus had at one time been in the body. None of the controls had the antibodies. A small percentage of the psychiatric patients did.

“We opened the sluice gate!” recalls one of the coauthors, Hilary Koprowski of Philadelphia’s Thomas Jefferson University. In the decade since, an array of papers have reported Borna virus antibodies turning up in anywhere from 4 to 40 per cent of patients under investigation: most often schizophrenics or people with unipolar or bipolar depression. Few of the controls had antibodies. But knowing exactly which studies to believe has proved tricky, says Ian Lipkin, a molecular biologist at the University of California at Irvine. “The assay is very subjective. A lot of the data are probably questionable.” Nonetheless, on balance Lipkin thinks that it’s likely that Borna does infect people, and possibly cause certain mental illnesses.

Meanwhile researchers were busy trying to nail the virus. For 60 years, they had known that Borna disease virus existed only because they could grow it in cells or in lab animals. That’s to say, when they mashed up the cells or the animals’ brains, the mix could trigger Borna disease in other animals. In all other senses the virus remained elusive. No one could find it under an electron microscope. No one knew how big it was, or if its genetic material was DNA or RNA. Then, in 1990, Lipkin found the first genetic traces of the virus, and by 1994, he and Ludwig’s groups, and de la Torre’s group working independently, had sequenced the entire viral genome. Borna virus has a single strand of RNA, and is a distant relative of the rabies virus, but is idiosyncratic enough to command its own, brand-new virus family.

Virus on the brain

Once the virus was cloned, the next sluice gate was flung open. Finding antibodies, after all, only takes you so far. It suggests that a person was once infected with the virus. But the antibodies may have been produced in response to another protein, only binding to the Borna virus by chance. Detecting a virus’s RNA or DNA is altogether more satisfactory. It’s a direct sign that the virus is in the body, here and now.

Certainly, after Bode and Ludwig found Borna disease virus RNA in depressed patients in 1995, at least four groups around the world reported that they, too, could find viral footprints in the blood of a small number of psychiatric patients, generally those with depression or schizophrenia. In some cases, more than half the patients harboured the virus, while none of the controls did. And in the past year, researchers have also found viral RNA in human cadaver brains, although not all of them were from people who were known to have suffered from mental disorders.

Heavy hints

De la Torre found the Borna virus in cadaver brains with damage to the hippocampus that could have been caused by virus. Lipkin found virus in brains of people who had suffered from schizophrenia, but not in the brains of people who had had other neurological problems. And a team led by Kazuhiko Ikeda, a neuropathologist at the Tokyo Institute of Psychiatry, discovered viral RNA in a small number of brains from people who had suffered from schizophrenia and Parkinson’s disease, as well as in normal brains.

The studies on brain and blood might hint that Borna virus can infect humans and possibly cause mental disorders, but the case is far from watertight. Studies tend to be small, and sometimes poorly designed. It doesn’t help, adds Lipkin, that in a field like this, rife with stiff competition and patents pending, “there is tendency to rush to publish”.

But that doesn’t mean that public health officials aren’t paying close attention. In 1995, a team led by virologist Kazuyoshi Ikuta at Hokkaido University in Sapporo, Japan, reported that five per cent of blood donors carried the Borna virus, raising the nasty spectre of depression by transfusion. “I went to the Centers for Disease Control in Atlanta last week, and they asked me, `What do we do?'” says Juergen Richt, a Borna researcher at the University of Giessen. “Because if this study is true, we have a big problem with the blood.”

Richt, for one, says he’s not too worried because he doesn’t believe the blood results. What makes Richt sceptical is a study that he and Koprowski reported in the April issue of the Journal of Neurovirology. The results suggested that labs routinely measuring Borna virus RNA were more likely to find it in blood than labs that never worked with the virus.

Richt points the finger at the method used to detect the viral RNA: reverse transcriptase PCR, exquisitely sensitive-and notoriously prone to contamination. “The technique can detect just a few molecules,” he says. “So if you have ten molecules on your pipette, or even in the air in your lab, you can have a false positive.” A second, as yet unpublished study, by a team led by virologist Peter Staeheli of the University of Freiburg also found little agreement between labs about which samples contain the virus, although few did.

But Ludwig is unmoved by the criticisms. He points to his three decades of experience with Borna. If other labs can’t find the virus, he says, perhaps their assays aren’t sensitive enough. Bode adds that her unpublished studies of Borna virus in the blood of people at different stages of bipolar disorder show that it only appears several weeks into an acute depressive episode. This could mean the virus is in the brain all along, but only leaks into the blood during times of rapid replication. That, rather than lab contamination or poor study design, could easily explain why different groups are turning up different results, she says.

As for the people who can’t replicate the amantadine findings, Ludwig and Bode say that they used the human strain of Borna virus in their own drug tests while everyone else has used strains from other animals. Then there’s human nature. Few Borna scientists could deny that in recent years their field has become characterised by competitiveness and bad feeling. “[They] are jealous that they have missed the Shinkansen. If they can’t repeat our work, that’s their problem,” says Ludwig.

And so the saga continues, with claims, counterclaims and not a little acrimony. “Why are you writing an article about Borna?” asks Koprowski, who has yet to be convinced that Borna can cause mental illness. “Why don’t you do something fun instead?” Still, there are reasons to suppose that the truth about Borna virus and human mental disorders will eventually emerge. Scientists are meeting and talking. They’re gearing up to do larger, more rigorous studies on the blood and brains of people with and without mental disorders. Others are calling for standardised methods of analysing Borna antibodies and virus, and pushing for freer exchange of lab materials, which would make the attempts to confirm-or refute-one another’s findings far easier.

In the meantime, there is definitely one disease that exposure to Borna produces. It manifests itself as confusion and the strongest urge to hold one’s head in one’s hand. And yes, a bit of depression.